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Date:      Thu, 24 Nov 2011 11:07:08 +0100
From:      Kees Jan Koster <>
Subject:   Re: Diagnosing packet loss
Message-ID:  <>
In-Reply-To: <>
References:  <> <>

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Dear All,

Thank you so much for the excellent suggestions. I can tell some of you =
have a lot of experience troubleshooting this issue.

At this stage I ruled out hardware or network issues. These are server =
grade network interfaces, new cables and the ifconfig configuration =
seems in order. netstat shows no collisions or packet errors for the =
past week or so.

I am dead certain there is no dupe IP. The other machines on the switch =
are currently off (test and load test box) and I still see packet loss. =
There simply is no other machine on the subnet that might have the same =

This seems to be local to my machine. Here is another reason why I say =
that: I can reliably transmit data when I bind to the aliased IP =
address: If I use mtr to measure packet loss from saffron (the stricken =
machine) to cumin (another machine in a different data center) I see the =

 saffron (ip address a) -> cumin: packet loss
 saffron (ip address b) -> cumin: no packet loss

 cumin -> saffron (ip address a): packet loss
 cumin -> saffron (ip address b): no packet loss

This is consistent from running mtr for 5 minutes straight. This to me =
shows that the hardware is fine. Using the alias IP address I can run =
with no packet loss for as long as I like.

Sooo.... Now what? I am completely at a loss. :-/
Kees Jan

I hate unit tests; I much prefer the illusion that there are no errors =
in my code.
                                                                 -- =
Hendrik Muller

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